JPS6090829A - Treatment of barium ferrite - Google Patents

Abstract

PURPOSE:To form barium ferrite having a favorable particle shape, superior dispersibility and blendability and suitable for use as a starting material for manufacturing a vertical magnetic recording medium by heat treatment at a relatively low temp. by mixing barium ferrite with a specified flux and heating the mixture to the m.p. of the flux or above. CONSTITUTION:One or more among a mixture consisting of KNO3 and NaNO3 in about 1:(0.3-3) molar ratio, a mixture consisting of CuCl and CaCl2 in about 1:(0.2-0.5) molar ratio and a mixture consisting of NaCl and CuCl in about 1: (1-3) molar ratio are used as a flux. Barium ferrite is mixed about 33-67wt% said flux, and the mixtur is heat treated at the m.p. of the flux or above, usually at about 250-450 deg.C in an atmosphere of a gas contg. oxygen for about 1- 10hr.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a treatment method for barium ferrite in which barium ferrite is mixed with a flux and heat treated to improve the particle shape dispersibility, orientation, etc. of barium ferrite.

Barium ferrite is often used as a raw material for ferrite rubber magnets, but in recent years it has attracted attention as a raw material for perpendicular magnetic recording media.

The methods for producing barium ferrite include (1) a dry method in which a mixture of iron oxide, barium carbonate, etc. is heated and fired at a high temperature of 1,100 to 1,400°C, and (2) a solution containing barium ions and iron ions with a pH of 8 or higher. Hydrothermal synthesis method by heating in an autoclave, (3) Direct generation of precipitate from a solution containing barium ions and iron ions, and heating the precipitate at 800°
Co-precipitation methods, etc., in which firing is performed at a high temperature of C or higher, are known.

The barium ferrite particles obtained by these methods differ slightly depending on the manufacturing method, but sometimes two particles are sintered or one particle is aggregated together.

In addition, the particles may have irregular shapes, and when they are used as raw materials for perpendicular magnetic recording media, for example, they have disadvantages of poor dispersibility and poor orientation.

Conventionally, as a method for improving the above-mentioned drawbacks of barium ferrite, there is a method of mixing barium ferrite with a flux and then heat-treating it at a temperature higher than the melting point of the flux. Japanese Patent Publication No. 55-1453
No. 04, JP-A-56-50200, JP-A-Sho 5
This method has been proposed in JP-A-6-73698, JP-A-56-92199, JP-A-56-1252'99, and the like.

However, in all of the conventionally proposed methods, it is necessary to perform heat treatment at a high temperature such that the melting point of the flux is high (approximately 900 to 1200 degrees Celsius).

An object of the present invention is to provide an improved method for treating barium ferrite, which involves mixing barium ferrite with a new flux and then heat-treating the mixture at a temperature equal to or higher than the melting point of the flux. Another object of the invention is.

It is an object of the present invention to provide a method for treating barium ferrite that can improve the single particle shape, 2 dispersibility, orientation, etc. without requiring high temperatures for heat treatment.

The object of the present invention is to provide barium ferrite with (A) a mixture of potassium nitrate and sodium nitrite, (B) a mixture of cuprous chloride and calcium chloride, and (0) a mixture of sodium chloride and cuprous chloride. This is achieved by a barium ferrite processing method characterized by mixing a flux selected from the group consisting of: heat treatment at a temperature higher than the melting point of the flux.

According to the present invention, the quality of barium ferrite can be improved at a low temperature of about 250 to 450°C.

The barium ferrite used in the present invention may be particles obtained by any method such as a dry method, a hydrothermal synthesis method, or a coprecipitation method. Further, some of the iron atoms of barium ferrite may be substituted with cobalt, titanium/indium, zinc, manganese, nickel, or the like.

The fluxing agents used in the present invention are a mixture of potassium nitrate and sodium nitrite, a mixture of cuprous chloride and calcium chloride, and a mixture of sodium chloride and cuprous chloride, each of which constitutes a fluxing agent. The mixing ratio (molar ratio) of the two types of compounds is generally KNO3:NaN02=1:0.
．． 3~31OuC4:CaCt2=1: 0.2~0
．． 5. NaCt: 0uC4=1: 1 to 3 is suitable. Furthermore, the melting point of each flux varies slightly depending on the mixing ratio of the two types of compounds.5For example, KNO3:NaN02=
In the case of 1:1, it is 220°C, CuC! t:0a042=
1: 400°C for 0.25, NaCt: 0u0
In the case of 7=1:3, the temperature is 14°C. The flux may be prepared by simply mixing both compounds, or by melting and mixing them.

What is the amount of flux to be mixed with barium ferrite?

A suitable amount is 66 to 67% by weight, preferably 50 to 60% by weight. If the amount of flux mixed in is too small, the quality improvement effect of barium ferrite tends to be insufficiently expressed, and if the amount mixed in is too large, the plate-like ratio of barium ferrite particles tends to increase. Since there is no particular advantage to increasing the amount, the above range is appropriate for the mixing amount. Note that it is also possible to mix multiple types of fluxing agents.

The method of mixing barium ferrite with a flux is not particularly limited, but generally a method of dry mixing barium ferrite powder particles and a powder flux is adopted.

Barium ferrite mixed with a flux needs to be heat-treated at a temperature higher than the melting point of the flux. When the heat treatment temperature is lower than the melting point of the flux, the specific surface area of barium ferrite is small, and when observed with a transmission electron microscope, the shape of each particle is irregular and aggregates, and many particles do not have a hexagonal plate shape. Tarishi.

Furthermore, when an organic binder is used in combination to form a magnetic recording medium layer, the dispersibility or orientation may be poor. The heat treatment temperature is not particularly limited as long as it is higher than the melting point of the flux, but if the temperature is too high, the advantage of being able to process at a low temperature will be lost.

Generally, heat treatment at about 250 to 450°C is appropriate. The heat treatment time is usually 1 to 10 hours, and the heat treatment is suitably carried out under an oxygen-containing gas atmosphere, such as an air atmosphere.

The heat-treated product is heated using a conventional method such as water.

After washing with an aqueous mineral acid solution and drying, barium ferrite powder particles having a uniform hexagonal plate shape and excellent dispersibility and orientation are obtained.

Example 1 Barium nitrate (B a (N 03
')2 '357.97 and ferric nitrate (Fe(N0
3) Add 39H20) 581.87 and dissolve by heating to about 80°C while stirring under a nitrogen atmosphere, and add 218.62 sodium hydroxide [NaOH] to this with 40% water.
0m1! A solution dissolved in is added dropwise under stirring to form a precipitate, held at 200'C for 1 hour in an autoclave, and further heated and held at 270'C for 1 hour to perform a hydrothermal synthesis reaction. The obtained precipitate was washed with water, filtered, then treated with dilute hydrochloric acid, washed with water, dried, and heated in an electric furnace at 700°.
C in an air atmosphere for 16 hours and pulverized to obtain barium ferrite crystal particles produced by hydrothermal synthesis. Observation of these barium ferrite crystal particles using a transmission electron microscope revealed that there was a lot of aggregation of two particles together, and the shapes of the two particles were irregular.

Next, 100 g of a flux (melting point: 220°C) having a molar ratio of potassium nitrate and sodium nitrite of 1:1 was mixed with the barium ferrite crystal particles 1002, and then heated in an electric furnace at 300°C in an air atmosphere for 3 hours. It was melted and heated, then rapidly cooled and solidified. The solidified product was then washed with warm water at about 60°C and dried to obtain barium ferrite crystal particles. Observation of the obtained barium ferrite crystal particles using a transmission electron microscope revealed that the crystal particles had a uniform hexagonal plate shape.

Each particle was separated and hardly any aggregated particles were observed.

Saturation magnetization (Bm) of this flux-treated barium ferrite
, coercive force (He), squareness ratio (Br73m), specific surface area (
The properties such as SA) were as shown in Table 1.

Further, flux-treated barium ferrite 107 was mixed with organic binder VAGH (trade name, manufactured by Union Carbide) 1.
3sr, dispersant stearic acid 0.47 and lecithin 0.25f, plasticizer polyurethane 2, OS', solvent methyl ethyl ketone 13, filter 52° methyl isobutyl ketone 1 filter, filter 57 and cyclohexanone 1135r,
and the hardening agent Coronate L (trade name 1 manufactured by Nippon Polyurethane Co., Ltd.) 0.49, mixed in a ball mill to form a paint, applied to a polyester film, dried, and the coercive force (
Hc) and squareness ratio (Br73m) were measured. The results are shown in Table 1.

Comparative Example 1 Table 1 shows the properties of the barium ferrite obtained in Example 1 before flux treatment and the properties after this barium ferrite was made into a paint in the same manner as in Example 1.

Example 2 Barium chloride [Ba0Q・2H20:] in 800 ml of water
43.77, ferric chloride [FeC1a 6H20]
140.6 f, cobalt chloride [:0oCA2・6
H20':l9',5F and titanium tetrachloride [:T
A solution containing iCA417.69 was added 20 Off of sodium hydroxide (NaOH) and 50 f! of sodium carbonate [Na2003]. was dissolved in 1,600 rrl of water, stirred at 60'C for 1 hour, filtered the formed precipitate, washed with water, dried, and calcined in an electric furnace at 900°C in an air atmosphere for 2 hours. Barium ferrite crystal particles were obtained by pulverization and a coprecipitation method. Observation of the barium ferrite crystal particles using a transmission electron microscope revealed that they were almost the same as in Example 1.

Next, the barium ferrite crystal particles 10f! After mixing a fluxing agent 107 with a molar ratio of potassium nitrate and sodium nitrite of 1:1, the mixture was heated in an electric furnace under an air atmosphere at a temperature of 30”.
The mixture was melted and heated at C' for 5 hours, then rapidly cooled and solidified. Next, the solidified product was washed with about 100 ml of warm water and dried to obtain barium ferrite crystal particles. Observation of the obtained barium ferrite crystal particles with a transmission electron microscope revealed that the crystal particles had a uniform hexagonal plate shape, each particle was separated, and hardly any aggregated particles were observed.

Characteristics and Example 1 of this flux-treated barium ferrite
The properties after being made into a paint in the same manner as above are shown in Table 2.

Comparative Example 2 Table 2 shows the properties of the barium ferrite obtained in Example 2 before flux treatment and the properties after this barium ferrite was made into a paint in the same manner as in Example 1.

Example 3 A fluxing agent (melting point 314°C) of sodium chloride and cuprous chloride in a molar ratio of 1:3 was mixed with barium ferrite crystal particles 10f obtained by coprecipitation method in the same manner as in Example 2. After that, it was melted and heated in an electric furnace at 400°C in an air atmosphere for 3 hours to obtain barium ferrite crystal particles in the same manner as in Example 1.

The results of observation of the barium ferrite crystal particles using a transmission electron microscope were almost the same as in Example 2. The properties after being made into a paint and the properties before being made into a paint are shown in Table 6 in the same manner as in Example 1.

Table 3 Example 4 A fluxing agent (melting point 400°C) 102 having a molar ratio of cuprous chloride and calcium chloride of 4:1 was added to the barium ferrite crystal particles 102 produced by the coprecipitation method in the same manner as in Example 2. After mixing, the mixture was melted and heated in an electric furnace at 450"C for 3 hours in an air atmosphere, and then rapidly cooled and solidified.
It was washed with warm water at 0°C and then dried to obtain barium ferrite crystal particles.

Characteristics after being made into a paint in the same manner as in Example 1.

The properties before being made into a paint are shown in Table 4.

Claims (2)

[Claims] (1) Barium ferrite from the group consisting of (A) a mixture of potassium nitrate and sodium nitrite, (B) a mixture of cuprous chloride and calcium chloride, and (c) a mixture of sodium chloride and cuprous chloride. A method for treating barium ferrite, which comprises mixing a selected flux and then heat-treating the mixture at a temperature equal to or higher than the melting point of the flux. (2) The method for treating barium ferrite according to claim 1, wherein the amount of the flux mixed is 33 to 67% by weight.